The boundaries of the reef regions
depicted in the maps is as defined in
the UNEP-WCMC atlas of coral reefs,Spalding (2001).

Image Database

NASA funding allowed IMaRS to complete the image database in 2005.
The NASA program provided substantial assistance with image acquisition. The main data
set is an archive of Landsat 7 images. The Landsat 7 satellite has been operational since
mid-1999 and has collected tens of thousands of coral reef scenes in the framework of the
Long Term Acquisition Plan (LTAP) of the
Landsat Program.
As participant to the Landsat Science Team, IMaRS advocated a specific acquisition
strategy for coral reefs and proposed a specific strategy using input from nearly 50
institutions worldwide that participate via the
NOAA Coral Health and Monitoring Program List-Server.
LTAP made this proposition a reality by implementing a plan for reefs in 1999
(Arvidson et al. 2001).
Using the existing global coral reef map produced by
(UNEP WCMC,
ReefBase),
we estimate that almost 900 Landsat scenes need to be processed to complete a global inventory
(Gasch et al. 2000).
The entire
Landsat 7 archive
is periodically inspected to identify the best image for one particular area.
As of 2007 the database contains more than 1700 Landsat 7 images. This premier Landsat 7 data set is complemented by a
substantial amount of Landsat 5 data acquired in the early nineties (mostly of the Caribbean
and Central America), by SPOT images (mostly of French coral reefs in the Pacific Ocean),
by several ASTER images (Red Sea and Pacific Ocean) and by a unique dataset of very high
spatial resolution IKONOS images. The
NASA Scientific Data Purchase Program (SDP)
provided the Landsat 5 and IKONOS images.

The principal data set consists of recent (1999-2002), generally cloud-free,
Landsat 7 ETM+ imagery. For images in which cloud cover is not optimal Landsat 5 TM, SPOT imagery
and/or International Space Station digital photographs have or will be used. The problem of
different acquisition dates between images is negligible because we mostly map geomorphological
zones that do not change, even on a decadal scale. Different spatial resolutions between images
also have only a minor impact
(Andréfouët et al. (2003)).

On an opportunistic basis, some very high-resolution data (aerial
photographs) are used to refine the interpretation of the Landsat images, but we do not
attempt to systematically collect archived aerial photographs. A selection of
IKONOS images
covering all kinds of reef configurations worldwide is also used to compare Landsat products
with higher resolution products
(Andréfouët et al. (2003)).
In addition, astronauts are continually increasing the new catalog of high-resolution (6 m)
digital photographs of coral reefs taken from the International Space Station
(Robinson and Evans, 2002),
which also allow validation of products.

The second data set is not directly used to map reefs, but to estimate
atmospheric parameters over the targets acquired by Landsat and to populate the
metadata-base of image processing parameters. We will use
SeaWiFS/MODIS images,
quasi-concurrent to Landsat 7 ETM+ overpasses to estimate aerosol types and their
contribution to the total signal. We will follow the method described in
Hu et al. (2001).